This invention relates to the field of rectifier assemblies used in engine-driven generators, such as automotive alternators, and more particularly, this invention relates to the field of manufacturing diode subassemblies used in such rectifier assemblies.
Press fit diode subassemblies are commonly used in vehicular extended thermal cycle minimal part robust rectifier assemblies, such as the type shown in commonly assigned U.S. Pat. No. 5,991,184, the disclosure which is hereby incorporated by reference in its entirety. These press fit diode subassemblies are formed as a subassembly of diode parts and press fitted within electrically conductive cooling plates of the rectifier assemblies. A stand-up diode lead extends upward from a diode cup that is usually press-fitted and interconnects various generator, e.g., alternator components. The press fit diode subassemblies include a lower cup, a silicon or other semiconductor diode die used as the diode or rectifying components, a stand-up diode lead, and an epoxy formed over the exposed diode lead and upper area of the cup. These types of rectifier assemblies using these diode subassemblies are produced throughout the United States and world, an example which is shown in the ""184 patent. A plurality, such as six press fit diode subassemblies, are manufactured for each rectifier such as that disclosed in the ""184 patent, although the number of diode subassemblies can vary depending on the type of rectifier and its end use.
The manufacturing techniques used in producing these press fit and similar diode subassemblies used in rectifiers are critical important and the techniques used can make a difference between a rectifier having a short life versus a longer life. Thus, it is critically important that the manufacturing processes of the diodes subassemblies be carefully monitored and controlled to obtain optimum diode production and rectifier operation.
It is therefore an object of the present invention to provide an improved method and process for manufacturing diode subassemblies used in rectifiers for engine-driven generators such as in automotive applications.
The present invention is advantageous and provides a diode subassembly manufacturing process that is advantageous and produces diode subassemblies with less oxidation and in a manufacturing environment that allows more critical specifications to be met.
In accordance with the present invention, a method of manufacturing a diode subassembly used in rectifiers for engine-driven generators is disclosed. The diode subassembly includes a diode cup and semiconductor diode die and diode leads fitted therein. In one aspect of the present invention, the method advantageously reflow solders a semiconductor diode die and diode lead within a diode cup in an argon/hydrogen atmosphere. This is advantageous over many prior art processes where a hydrogen or nitrogen atmosphere is used.
In yet another aspect of the present invention, solder preforms are inserted between the diode cup and semiconductor diode die, and the diode lead and semiconductor diode die before reflow soldering. Reflow soldering can occur within an argon/hydrogen atmosphere of about 80% argon and 20% hydrogen. The step of reflow soldering can be at a temperature up to about 400xc2x0 C. The step of reflow soldering can occur under pressure to aid in forcing the semiconductor diode die, diode cup and diode lead together.
In yet another aspect of the present invention, the step of reflow soldering can occur at a pressure up to about 60 pounds per square inch. The step of reflow soldering can occur with a lead-tin-indium solder. The step of reflow soldering can also comprise the step of sealing the diode cup, semiconductor diode die and diode lead with a sealant, such as epoxy.
In yet another aspect of the present invention, the method of manufacturing a diode assembly of the present invention comprises the steps of positioning a diode cup within a die boat having a plurality of soldering positions for holding diode cups therein. A lead loader has a removable lead holder that holds diode leads within the lead loader. The lead loader is positioned over the diode boat such that the diode leads are aligned with respective diode cups. The lead holder is removed from the lead loader such that the diode leads fall into the center cups, which also have the semiconductor diode die positioned therein. The die boat is positioned within an oven and the semiconductor diode die and diode lead are soldered within the diode cup in an argon/hydrogen atmosphere of the oven.